On NETTUTS.com a new series of vidcasts has started up introducing the CodeIgniter framework (the first of ten parts):

After numerous requests, today we are launching a new screencast series on Nettuts+ that will focus exclusively on the CodeIgniter PHP framework. Over the course of about 10 videos, I'll teach you exactly how to use this framework. Ultimately, we'll work our way up to building a custom CMS. Without further ado, here's day one!

The video (which is also available on iTunes in a higher quality) lays down some of the fundamentals - what the framework is, how its structured and some examples of how it can be used. You can also download the source for all of the examples in the video.